Adaptive link quality management for wireless medium

ABSTRACT

To provide the quality and reliability of a fiber optic link over a wireless link, network nodes in accordance with the present invention include a link quality management unit, which controls multiple transmission parameters of a wireless interface in response variable link conditions. For example, the link quality management unit of one embodiment of the present invention controls transmission power, modulation, and error correction. In general, a receiving network node provides feedback to a transmitting network node. Thus, in many embodiments of the present invention, the link quality management unit includes a signal quality detector, which measures a signal quality value, such as bit error rate, signal to noise ratio, or error vector magnitude. The measured signal quality is transmitted back to the transmitting node so that appropriate changes can be made to the transmission parameters.

RELATED APPLICATIONS

[0001] The present application is a continuation-in-part of U.S.Provisional Patent Application Serial No. 60/256,540, by ChandrasekaranNageswara Gupta, Addepalli Sateesh Kumar, and Tushar Ramanlal Shah,entitled “Packet-Based Dual-Ring Broadband Wireless Network” filed Dec.18, 2000, which is incorporated herein by reference.

[0002] The present application is also a continuation-in-part of U.S.Provisional Patent Application Serial No. 60/276,610, by Tushar RamanlalShah, Addepalli Sateesh Kumar, and Chandrasekaran Nageswara Gupta,entitled “Architecture Optimized to Support Fixed-Rate SynchronousNative TDM Data (SONET) and Bursty Asynchronous Data Transmission overMetropolitan Area Network Using Any Physical Medium Including But NotLimited to Optical or Wireless Medium” filed Mar. 16, 2001, which isincorporated herein by reference.

[0003] This application also relates to concurrently filed, co-pendingapplication Ser. no. ______ [Docket No: RNI-001], by Gupta et. al,entitled “Network Node with Multi-Medium Interfaces”, owned by theassignee of this application and incorporated herein by reference.

[0004] This application also relates to concurrently filed, co-pendingapplication Ser. no. ______ [Docket No: RNI-002], by Kumar et. al,entitled “Hybrid Network to Carry Synchronous and Asynchronous Trafficover Symmetric and Asymmetric Links”, owned by the assignee of thisapplication and incorporated herein by reference.

[0005] This application also relates to concurrently filed, co-pendingapplication Ser. No. ______ [Docket No: RNI-003], by Kumar et. al,entitled “Dynamic Mixing of TDM Data with Data Packets”, owned by theassignee of this application and incorporated herein by reference.

[0006] This application also relates to concurrently filed, co-pendingapplication Ser. No. ______ [Docket No: RNI-005], by Shah et. al,entitled “Integration of Network, Data Link, and Physical Layer to AdaptNetwork Traffic”, owned by the assignee of this application andincorporated herein by reference.

[0007] This application also relates to concurrently filed, co-pendingapplication Ser. no. ______ [Docket No: RNI-006], by Kumar et. al,entitled “Method of Generating, Transmitting, Receiving and RecoveringSynchronous Frames with Non-standard Speeds”, owned by the assignee ofthis application and incorporated herein by reference.

FIELD OF THE INVENTION

[0008] The present invention relates to data networking. Morespecifically, the present invention relates to network nodes usingmultiple network mediums in metro area networking.

BACKGROUND OF THE INVENTION

[0009] The development of high-speed networking has traditionally beendriven by the telecommunications industry and the computer industry.However the data traffic patterns for the telecommunications industry isvery different from the data traffic pattern for the computer industry.Specifically, the telecommunication industry primarily has beenconcerned with providing data networks for carrying voice data intelephone calls. Voice data in general requires a constant bandwidthconnection. Thus, the telecommunication networks were traditionallydesigned to provide constant bandwidth using time division multiplexing(TDM) techniques. In time division multiplexing each data stream isassigned a specific amount of bandwidth within the TDM network totransfer data. For example, synchronous optical network (SONET/SDH/PDH)is a widely used networking scheme in the telecommunications industry.SONET/SDH/PDH is a connection oriented scheme, in which each channel isgiven a fixed amount of bandwidth based on a standardized incrementrelated to the amount of data needed to provide a standard voice phonecall. Furthermore, TDM networks for voice-based applications aretypically designed to support peak usage bandwidth requirements. Thus,under normal circumstances (i.e. non-peak usage) TDM networks are underutilized and have spare capacity.

[0010]FIG. 1 shows a typical TDM based metro area network (MAN) 100having various network nodes 110, 120, 130, 140, 150, and 160 connectedwith fiber optic links 112, 121, 123, 132, 134, 143, 145, 154, 165, 156,116, and 161. Specifically, network node 110 is coupled to network node120 by fiber optic links 121 and 112. Fiber optic link 112 carries datafrom network node 110 to network node 120. Fiber optic link 121 carriesdata from network node 120 to network node 110. In general fiber opticlink 1xy carries data from network node 1x0 to network node 1y0, where xand y are in the range 1-6 inclusive. Typically, each network nodeprovides TDM service to large number of users, who are coupled to thenetwork node using industry standard TDM interfaces. Fiber optic linksare used because of the high bandwidth, low latency, reliability, andconsistency provided by fiber optic links as compared to other networkmedium. Metro area network 100 uses a dual ring topology. The dual ringtopology provides redundancy in case one of the optical links becomesunusable. For example, if optical fiber link 123 were to becomeunusable, data from network node 120 could still reach network node 130using fiber optic links 121, 116, 165, 154, and 143.

[0011]FIG. 2 is a simplified block diagram of a conventional networknode 200 having a first optical interface 210, a second opticalinterface 220, a TDM user interface 230, and a cross connect unit 240.Optical interfaces 210 and 220 are configured to transmit and receivedata with other network nodes. Specifically, each optical interfaceincludes a fiber optic port for a transmit fiber optics link (not shown)and a receive fiber optics link (not shown). For example, if networknode 200 were used in place of network node 120 (FIG. 1) opticalinterface 210 would be coupled to fiber optic links 112 and 121 andoptical interface 220 would be coupled to fiber optics link 123 and 132.TDM user interface 230 provides an access point for receiving andtransmitting data to user equipment or networks. Various embodiments ofnetwork node 200 may provide TDM user interfaces with different networkmedium and protocols. Data from TDM user interface 230 is transferred tooptical interfaces 210 and/or 220 through cross connect unit 240.Conversely, data destined for the users of network node 200 are receivedby optical interfaces 210 and/or 220 and transferred to TDM userinterface 230 through cross connect unit 240.

[0012] TDM networks transfer data in TDM frames like SONET, SDH, andPDH. SONET refers to Synchronous Optical Network. SDH refers toSynchronous Digital Hierarchy. PDH refers to Plesiochronous DigitalHierarchy. FIG. 3 shows an example of a TDM frame 300, which is made ofheader columns and payload columns. TDM frame 300 could be for example aSONET frame, a SDH frame or a PDH frame. TDM Frame 300 includes a headersection 310 and payload columns such as columns 321, 325, and 327.Header section 310 contains information regarding TDM frame 300 such asthe source and destination of TDM frame 300. The payload columns containpayload data to be transported. Payload data is also referred to as thetransport payload. In general TDM frame 300 has a fixed number of datacolumns. For example, a SONET STS1 frame consists of 90 columns of 9bytes each. The first three columns form header section 310 leaving 87payload columns (and a byte space of 87×9 bytes) for payload. An STSnframe contains first 3xn columns of header and 87xn columns for payload.Transport payload size varies. Thus sometimes the transport payload doesnot occupy all of the 87n payload columns. Other times, the transportpayload may spill over to a part of the payload columns of the followingTDM frame. A transport payload may start at any byte in the payloadcolumns of the TDM frame. The transport payload is packed into thepayload columns in a column-wise manner and is provisioned in anintegral number of columns in the TDM frame. If the TDM frame is notprovisioned to full capacity, the unprovisioned columns, i.e. unusedcolumns, are filled with dummy (non-data) characters. Thus, some of thetotal bandwidth of a TDM network may be unused during normal operation.

[0013] The computer industry primarily is concerned with transferringcomputer data over a network. In general, computer data is “bursty”,i.e., computer data traffic requires high bandwidth for some periods oftimes and little or no bandwidth at other times. To take advantage ofhigh-speed networks, the computer industry adopted a packet-basedapproach to networking. Generally, a data stream is packetized intomultiple data packets. The data packets contain identifying informationso that the packets can be reassembled into the original data stream.Packet based networking allows multiple data streams to share a networkand obtain better bandwidth utilization for bursty data than the TDMapproach used in telecommunication networks.

[0014] With the growing use of computers and computer networks, inparticular the Internet, the amount of computer data traffic isincreasing very rapidly. In contrast, voice data traffic is growing at aslower pace. Furthermore, some voice data is being transformed intopacket data using protocols such as Voice over Internet Protocol (VoIP).To capitalize on the growing use of packetized data, techniques andequipment need to be developed to allow efficient transport ofpacketized data on TDM networks having excess capacity.

[0015] Additionally, deployment limitations of typical TDM networksprevent wide spread use of TDM networks for TDM and Computer networkapplication. As explained above, the telecommunication/computer networksmake use of fiber optic links for increased bandwidth and reliability.However, installation of fiber optic cables particularly in ametropolitan area is very time consuming. For example to add fiber opticlinks to a new network node, trenching permits and easements must beobtained prior to installing and configuring the optical links.Including the time required to obtain permits and easements, the time toactually install and configure a fiber optic link to a new network nodecould be as long as 18 months. Given all the regulatory challenges andthe cost of deploying fiber, fiber is deployed to only 8-10% ofbuildings in dense urban areas like Manhattan, N.Y. and less than 1% indense suburban areas like San Jose, Calif. The long delay in obtainingconnections to a network node cannot be tolerated in the fast pacedcomputer industry. Hence, there is a need for a method and system tocombine packet based data with TDM data and to overcome the deploymentlimitation of fiber optic based networks.

SUMMARY

[0016] Accordingly, a network node in accordance with some embodiment ofthe present invention provides wireless interfaces with the quality andreliability of fiber optic interfaces. Furthermore, network nodes inaccordance with some embodiments of the present invention can combinedata packets within TDM data frames to provide support for both TDM dataand packet data.

[0017] For example, in one embodiment of the present invention a networknode includes a network interface, a cross connect switch coupled to thenetwork interface, and a multi-medium network interface coupled to thecross connect switch. The multi-medium network interface includesmultiple network interfaces, such as an optical interface and a wirelessinterface. The wireless interface could be for example an RF wirelessinterface or a free-space optics interface. Some embodiments of thepresent invention may include both an RF wireless interface and afree-space optics interface. A TDM user interface is also coupled to thecross connect switch. In some embodiments, the network interface is alsoa multi-medium network interface. Furthermore, some embodiments caninclude additional multi-medium network interfaces.

[0018] As stated above, some embodiments of the present invention allowTDM data to be combined with packet data. A Packet/TDM cross connectswitch, having both a TDM switch and a packet switch, is used in theseembodiments. Data packets are transformed into TDM packet columns. TheTDM packet columns are combined with standard TDM data columns in thepayload of a TDM data frame. Data packets may be sorted based on apriority scheme, in which high priority data packets are givenprecedence over lower priority data. However, both high priority and lowpriority may be combined in a TDM packet column

[0019] To provide the quality and reliability of a fiber optic link overa wireless link, many embodiments of the present invention include alink quality management unit, which controls multiple transmissionparameters of a wireless interface in response variable link conditions.For example, the link quality management unit of one embodiment of thepresent invention controls transmission power, modulation, and errorcorrection. In general, a receiving network node provides feedback to atransmitting network node. Thus, in many embodiments of the presentinvention, the link quality management unit includes a signal qualitydetector, which measures a signal quality value, such as bit error rate,signal to noise ratio, or error vector magnitude. The measured signalquality is transmitted back to the transmitting node so that appropriatechanges can be made to the transmission parameters.

[0020] To provide even greater quality of service, some embodiments ofthe present invention use a media abstraction unit to integratelink-layer management with network layer traffic management. Asexplained above, various transmission parameters are modified inresponse to changing environmental factors. The modification of thetransmission parameters changes the available bandwidth of the wirelesslink. In accordance with some embodiments of the present invention, theavailable bandwidth of the wireless link is used at network layertraffic management. Specifically in one embodiment of the presentinvention, the amount low priority data packet within a TDM data frameis altered to use the available bandwidth.

[0021] The rigid bandwidth hierarchy of conventional TDM protocols isnot suited for fully using the available bandwidth of a wireless link.Thus, many embodiments of the present invention use TDM frames that havepayloads, which do not strictly conform to the bandwidth hierarchy ofconventional TDM protocols. For example, many embodiments of the presentinvention form TDM frames having a payload that is a non-integermultiple of a base bandwidth, such as OC-1/STS-1.

[0022] The versatility provided by network nodes in accordance with thepresent invention allows the formation of networks using different typesof links, links with differing bandwidth, data rates, and bit errorrates, as well as both asymmetric and symmetric links. For example, anetwork can include a first network node coupled to a second networknode with a wireless link. The network can include a third network nodecoupled to the second network node an optical link and coupled to thefirst network node by a wireless link. A fourth network node can beeasily inserted between the third network node and the third networknode using wireless links. The optical link between the second and thirdnetwork nodes can operate at one bandwidth and the various wirelesslinks would operate at other bandwidths depending on the environmentalconditions between each pair of nodes.

[0023] The present invention will be more fully understood in view ofthe following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a block diagram of a typical TDM (SONET/SDH/PDH) basednetwork.

[0025]FIG. 2 is a simplified block diagram of a conventional networknode.

[0026]FIG. 3 is a conventional TDM frame.

[0027]FIG. 4 is a simplified block diagram of a network node inaccordance with one embodiment of the present invention.

[0028]FIG. 5 is a block diagram of a network using multi-medium networknodes in accordance with one embodiment of the present invention.

[0029]FIG. 6 is a block diagram of a network using multi-medium networknodes in accordance with one embodiment of the present invention.

[0030]FIG. 7(a) is a simplified block diagram of a network node inaccordance with one embodiment of the present invention.

[0031]FIG. 7(b) is a simplified block diagram of a network node inaccordance with one embodiment of the present invention.

[0032]FIG. 8 is a block diagram of a multi-medium network interface inaccordance with one embodiment of the present invention.

[0033]FIG. 9 is a block diagram of a free space optics network interfacein accordance with one embodiment of the present invention.

[0034]FIG. 10 is a block diagram of a radio frequency wireless networkinterface in accordance with one embodiment of the present invention.

[0035]FIG. 11(a) is a block diagram of one embodiment of a TDM Crossconnect unit/Packet switch.

[0036]FIG. 11(b) is a block diagram of one embodiment of a TDM Crossconnect unit/Packet switch.

[0037]FIG. 12 is a diagram of a partially filled SONET frame, that is,fractional OC-X in accordance with one embodiment of the presentinvention.

[0038]FIG. 13 is a block diagram of a link quality management unit inaccordance with one embodiment of the present invention.

[0039]FIG. 14 is a block diagram of an error correcting code unit inaccordance to one embodiment of the present invention.

DETAILED DESCRIPTION

[0040] As explained above, conventional TDM networks are inefficient interms of bandwidth utilization. Adapting TDM networks for bursty packetbased data from computer networks can achieve higher bandwidthutilization. However, deployment of additional conventional networknodes limited to fiber optic links is time consuming and expensive.Thus, in accordance with one embodiment of the present invention, amulti-medium network node is configured to support TDM network protocolssuch as SONET/SDH/PDH. Furthermore, network node in accordance with someembodiments of the present invention support dynamic multiplexing ofpacket based data with TDM data into TDM SONET/SDH/PDH frames for usewith conventional TDM networks nodes and equipment.

[0041]FIG. 4 is a simplified block diagram of a multi-medium networknode 400 in accordance with one embodiment of the present invention.Multi-medium network node 400 includes a first multi-medium interface410, a second multi-medium interface 420, a TDM user interface 430, anda cross connect unit 440. Multi-medium interfaces 410 and 420 allowdifferent physical medium to be used between network nodes. For example,in one embodiment of the present invention multi-medium interface 410 isconfigured to transfer data using fiber optic links and/or wirelessnetwork links. TDM user interface 430 provides an access point forreceiving and transmitting packet or TDM data to user equipment ornetworks. Various embodiments of multi-medium network node 400 mayprovide TDM user interfaces with different network medium and protocols.Data from TDM user interface 430 is transferred to multi-mediuminterface 410 and/or 420 through cross connect unit 440. Conversely,data destined for the users of multi-medium network node 400 arereceived by multi-medium interfaces 410 and/or 420 and transferred toTDM user interface 430 through cross connect unit 440. Other embodimentsof the present invention may include additional multi-medium interfacesto allow a multi-medium network node to simultaneously communicate withmore than two other network nodes. Multi-medium interface 410 and 420,cross connect unit 440 and TDM user interface 430 are described indetail below.

[0042] Another embodiment of the present invention relates to asymmetricnetworking, in which multi-medium network node 400 interfaces to mediumswith attributes differing in type of physical medium, link rates,protection mechanisms etc. For example the first multi-medium interface410 may interface to an optical fiber at OC-48 rate using UnidirectionalPath-Switched Ring (UPSR) or Bi-directional Line-Switched Ring (BLSR)protection for TDM and Intelligent Protection Switching (IPS) protectionfor packet, whereas the second multi-medium interface 420 interfaces toa wireless medium operating at OC-12 rate.

[0043]FIG. 5 illustrates a ring network 500 adding multi-medium networknodes in accordance with one embodiment of the present invention.Because network 500 is similar to network 100 (FIG. 1) the descriptionof unchanged elements is not repeated. In network 500 network nodes 120and 130 are replaced with multi-medium network nodes 520 and 530,respectively. Multi-medium network node 520 communicates with networknode 110 using conventional fiber optic links 112 and 121. Similarly,multi-medium network node 530 communicates with network node 140 usingconventional fiber optic links 134 and 143. A Multi-medium network node570 can be inserted between multi-medium network node 520 and 530without the time and expense of installing fiber optic links tomulti-medium network node 570. Specifically, multi-medium network node570 communicates with multi-medium network node 520 and 530 usingbi-directional wireless links 527 and 537, respectively. As explainedbelow, multi-medium network nodes in accordance with differentembodiments of the present invention can use different types of wirelesslinks, such as RF (radio frequency) wireless links or free space opticslinks. Thus, additional network nodes can be easily added toconventional TDM networks without the time and cost of actuallyinstalling fiber optic links. If fiber optic links are still desired,multi-medium network nodes 520, 530, and 570 can be configured to firstuse wireless links and then change to the fiber optic links after theyare installed. Furthermore, the multi-medium network nodes can beconfigured to use both the fiber optic links and the wireless links toincrease bandwidth. Alternatively, the multi-medium network node can beconfigured to use the wireless link as a backup link when thefiber-optic link is unavailable. Also as explained below, embodiments ofthe present invention can replicate the redundancy of the dual ringarchitecture of conventional TDM networks when using wireless links.Because multi-medium network nodes in accordance to the presentinvention can be used with a variety of network mediums, embodiments ofthe present invention can be used in both homogenous and heterogeneousnetworks. For example, multi-medium network nodes can be used innetworks having only fiber optic links between network nodes, networkshaving only wireless links between network nodes, and networks havingboth fiber optics and wireless links between network nodes. Furthermore,some embodiments of the present invention support both links havingsymmetrical attributes and links having asymmetrical attributes.

[0044] Some embodiments of the present invention include automaticconfiguration of new network nodes. In these embodiments, a new nodelink admission procedure is used to establish the links of the newnetwork node. For example, in some embodiments of the present invention,new network nodes (or network nodes recovering from a link failure), areconfigured transmit a link connect request signal. The pre-existingnetwork node is configured to respond with a link connect response. Insome networks, a network operation center is used to configure thenetwork nodes and to accept or reject new network nodes. Furthermore,some network nodes use authentication protocols to insure the newnetwork node is acceptable to the network. After receiving the linkconnect response, the new network node transmits a link connectacknowledgement to activate the link.

[0045]FIG. 6 illustrates a mesh network 600 using multi-medium networknodes in accordance with another embodiment of the present invention.Specifically mesh network 600 includes multi-medium network nodes 610,620, 630 and a conventional network node 640. Each multi medium networknode in mesh network 600 includes three multi-medium interfaces, so thateach multi-medium network node can be coupled to three other networknodes. Similarly, network node 640 includes three optical interfaces.Conventional network node 640 is coupled to multi-medium network nodes610, 620, 630 using fiber optics links 614 and 641, fiber optic links624 and 642, and fiber optic links 643 and 634, respectively.Multi-medium network node 610 is also coupled to multi-medium networknodes 620 and 630 using bi-directional wireless links 612 and 613,respectively. Multi-medium network node 620 is also coupled tomulti-medium network node 630 by bi-directional wireless link 623.Multi-medium network nodes in accordance with the present invention canalso be used in other network topologies, such as point-to-point andstar topologies.

[0046]FIG. 7(a) is a block diagram of a multi-medium network node 700 ain accordance with another embodiment of the present invention. Becausemulti-medium network node 700 a is similar to multi-medium network node400, the description of unchanged elements is not repeated. However,multi-medium network node 700 a differs from multi-medium network node400 by including a packet user interface 730 and replacing cross connectunit 440, with a Packet/TDM cross-connect unit 740. Packet/TDM crossconnect unit 740 allows packet processing and dynamic mixing of TDM andPacket data. Packet user interface 730 receives and transmits datapacket as used in packet-based networks such as Ethernet, IP, or otherpacket based networks. Data packets from packet user interface 730 aretransferred to Packet/TDM cross connect unit 740 which dynamically mixesthe packet data and TDM payload from TDM user interface 430 into TDMframes, such as SONET, SDH, or PDH frames, for transfer throughmulti-medium interface 410 or 420. Conversely, when data is received onmulti-medium interface 410 or 420, Packet/TDM cross connect unit 740decodes the TDM frames to demultiplex the packet data from the TDM data.Packet data is transferred to packet user interface 730 and TDM data istransferred to TDM user interface 430.

[0047] Packet/TDM cross connect unit 740 provides the transport pathsfor various interfaces of multi-medium network node 700 a. Generally,Packet/TDM cross connect unit 740 receives payload from each interfaceand routes the payload to the appropriate interface. For example,received payload from multi-medium interface 410 may be destined formulti-medium interface 420, TDM user interface 430, or packet userinterface 730. Similarly payload from multi-medium interface 420 may bedestined for multi-medium interface 410, TDM user interface 430, orpacket user interface 730. Data from TDM user interface 430 may bedestined for multi-medium interface 410 or multi-medium interface 420.Similarly, data from packet user interface 730 may be destined formulti-medium interface 410 or multi-medium interface 420. Furthermore,the payload from one user on TDM user interface 430 may be destined toanother user on TDM user interface 430 rather than being destined formulti-medium interface 410 or multi-medium interface 420. Similarly,packet data from a user of packet user interface 730 may be destined toanother user of packet user interface 730 rather than being destined formulti-medium interface 410 or multi-medium interface 420.

[0048] Because, multi-medium network node 700 a is designed for use in aTDM network, Packet/TDM cross connect unit 740 is configured to receive,process, and dispatch TDM frames from and to multi-medium interface 410and multi-medium interface 420. Specifically, when a TDM payload of aTDM frame is received from multi-medium interface 410, Packet/TDM crossconnect unit 740 must process the TDM payload to determine which partsof the TDM payload are “DROP Payload” and which parts are “THROUGHPayload.” DROP payload refers to payload destined to users ofmulti-medium network node 700 a that are coupled to Packet/TDM crossconnect unit 740 through TDM user interface 430 or packet user interface730. THROUGH payload refers to payload that is destined for othernetwork nodes and is thus sent through multi-medium interface 420. Datafrom TDM user interface 430 or packet user interface 730 that aredestined to multi-medium interface 420 are often referred to as “ADDpayload” because the data can be added to a TDM frame. TDM frames frommulti-medium interface 420 are treated similarly.

[0049]FIG. 7(b) is a block diagram of a multi-medium network node 700 bin accordance with another embodiment of the present invention. Becausemulti-medium network node 700 b is similar to multi-medium network node700 a, the description of unchanged elements is not repeated. However,multi-medium network node 700 b differs from multi-medium network node700 a by including multiple multi-medium interfaces 410_1, 410_2, . . .410_N, 420_1, 420_2, . . . 420_M, where N and M are integers. Includingmultiple multi-medium interfaces allows more complicated networktopologies, such as a mesh topology, star topology, subtending ringtopology, multi-ring topology, or tree topology.

[0050]FIG. 8 is a block diagram of a multi-medium interface 800 (block410 or 420 in FIG. 7(a)) having a fiber optics port and two wirelessports. Specifically, multi-medium interface 800 includes a fiber opticsport 825, a free-space optics port 835 and a RF wireless port 845. Otherembodiments of multi-medium interface in accordance with the presentinvention may use a different number of ports and different types ofports. For example some embodiments of the present invention may omitfiber optics port 825. Furthermore, different multi-medium interfaces ona multi-medium network node may have different ports. For example, amulti-medium network node in accordance with one embodiment of thepresent invention uses a standard fiber optics interface and only onemulti-medium interface.

[0051] Multi-medium interface 800 includes a physical layer interface(PHY LAYER Interface) 810, which interfaces with cross connect unit 440(FIG. 4) or Packet/TDM cross connect unit 740 (FIG. 7(a) and FIG. 7(b)).Physical layer interface 810 is coupled to optical transceiver 820.Specifically, parallel data from cross connect unit 440 or Packet/TDMcross connect unit 740 is converted into a serial bit stream for opticaltransceiver 820. Conversely, physical layer interface 810 convertsserial data from optical transceiver 820 into parallel data for crossconnect unit 440 or Packet/TDM cross connect unit 740.

[0052] Optical transceiver 820 transforms data received from physicallayer interface 810 into an optical data stream to be transmitted at thefiber optics port 825. Optical transceiver 820 also transforms opticaldata received from fiber optics port 825 into serial format used byphysical layer interface 810.

[0053] Media abstraction unit 850 enables the optical signal fromoptical transceiver 820 to seamlessly interface with other types oflinks, such as RF wireless medium and free-space optical medium. Mediaabstraction unit 850 includes a transmit path and a receive path. Thetransmit path of media abstraction unit 850 converts optical signal fromoptical transceiver 820 into an electrical data stream and reframes thedata stream into a stream of electrical data frames that has a sizeparticularly suited for wireless transmission. For example, in oneembodiment of the present invention, media abstraction unit 850 reframesthe data stream into data frames having a size of 255 bytes, which iswell suited for RF wireless transmission. Media abstraction unit 850determines the level of modulation for RF wireless unit 840 and thetransmission power and level of coding for free-space optics unit 830and RF wireless unit 840 using one or more link quality management unitsdescribed below. Media abstraction unit 850 adjusts these parameters,which may change the capacity of the wireless link in response tochanging environmental conditions. Electrical data frames from mediaabstraction unit 850 are converted into radio frequency signal by RFwireless unit 840 or into laser optical signal by the free-space opticsunit 830. The receive path of media abstraction unit 850 reframeselectrical data frames from RF wireless unit 840 or free-space opticsunit 830 into TDM frames such as SONET/SDH/PDH frames and then convertsthe data stream into an optical signal. The optical signal is sent tooptical transceiver 820 and then to physical layer interface 810.

[0054] As stated above, media abstraction unit 850 adjusts parameters ofthe wireless links between multi-medium network nodes, such as themodulation, transmission power and coding of the data stream in responseto environmental conditions. Specifically, media abstraction unit 850 inthe receiving multi-medium network node provides feedback to mediaabstraction unit 850 in the transmitting multi-medium network node. Inone embodiment of the present invention, feedback is provided usingcontrol packet containing the dynamic status of link characteristicssuch as the received bit error rate, signal to noise ratio, power level,etc. The dynamic characteristics of wireless link are affected byfactors like attenuation, phase distortion, noise, interference,scintillation, beam wandering, etc. Furthermore, atmospheric factorssuch as rain, snow, and fog may affect the link characteristics verysignificantly. Media abstraction unit 850 dynamically adjusts theattributes of the transmitted wireless signal such as the power,modulation, and coding to combat variation in link characteristics. Forexample, deterioration in link characteristics may be minimized byincreasing the transmitted power or changing the digital modulation froma high 256-QAM to 16-QAM level. Additionally the transmitted power canbe controlled automatically using the feedback information provided toMedia abstraction unit 850. Generally, Media abstraction unit 850adjusts the attributes of the transmitted signal without degradation ofthe data flow on the wireless link.

[0055] Media abstraction unit 850 unit renders the wireless linkstransparent to the rest of the multi-medium network node at the sametime makes the networking layer aware of the dynamic status of thewireless medium. As a result, the wireless links (both free space opticsand radio frequency wireless) are as reliable as fiber optic links. Insome embodiments, media abstraction unit 850 recovers the clockingsignals in TDM systems such as, SONET, SDH, or PDH from a non-opticalmedium such as the wireless or free-space optical medium.

[0056] In the specific embodiment illustrated in FIG. 8, radio frequencywireless unit 840, free space optics unit 830, and the media abstractionunit 850 interfaces with optical transceiver 820 rather than directlywith physical layer interface 810. Because media abstraction unit 850 iscoupled to optical transceiver 820 using fiber optic links, mediaabstraction unit 850 and optical transceiver 820 can be placed farapart. For example, the portions of a multi-medium network nodeincluding optical transceiver 820 may be located inside a building andother portions of the multi-medium network node including mediaabstraction unit 850 may be located at rooftop or on a window of thesame or another building.

[0057] RF wireless unit 840 receives the stream of electrical dataframes from media abstraction unit 850 and broadcasts the data throughRF wireless port 845. RF wireless units 840 also receives data throughRF wireless port 845 and transform it into a stream of electrical dataframes for media abstraction unit 850. In some embodiments of thepresent invention, RF wireless unit 840 uses a first frequency fortransmitting data and a second frequency for receiving data.

[0058] Similarly, free space optics unit 830 transforms the stream ofelectrical data frames received from media abstraction unit 850 into anoptical format for free space optics port 835. Free-space optics unit830 also transforms optical data received from free-space optics port835 into the stream of electrical data frames for media abstraction unit850.

[0059]FIG. 9 is a block diagram of a free space optics unit 900 that canbe used as free-space optics unit 830 (FIG. 8). Free-space optics unit900 includes one or more free-space optics transmitters 910_T1 to 910_TN(N may be greater than 1), a frees-pace optics receiver 910_R, opticalfibers 924, optical fiber 926, beam collimators 930_1 to 930_N, and abeam receptor 940. Each free-space optics transmitter 910_Ti to 910_TNreceives the same stream of electrical data frames from mediaabstraction unit 850 and converts the stream of electrical data framesinto an optical signal. Each Beam collimator 930_1 to 930_N collimatesoptical signal from free-space optics transmitter 910_T1 to 910_TN,respectively, into a laser beam of a fixed aperture diameter and a smalldivergence angle. Optical assembly (not shown) of beam collimator 930_1to 930_N transmits the laser beams in free space between network nodes.Generally, the aperture diameter and divergence angle are selected tobase on the atmospheric conditions of the free space between the networknodes. Increasing the aperture diameter increases the power received atthe receptor. Decreasing the beam divergence angle decreases the size ofthe footprint of the laser beam at the receptor, which increases thepower received. However, a smaller footprint of the laser beam reducesthe margin of tolerance of the beam wandering. Using multiple laserbeams minimizes signal loss due to scintillation and other disruptionsof line of sight transmission between two network nodes. Someembodiments of the present invention use spatial diversity with themultiple transmitted laser beams so that small flying objects such asbirds do not disrupt the free-space optics link.

[0060] Beam receptor 940 receives one or more laser beams from anothernetwork node and focuses the beams onto an optical fiber 926. Opticalfiber 926 provides optical signal to free-space optics receiver 910_R,which transforms the optical signals into a stream of electrical dataframes for media abstraction unit 850. For embodiments of the presentinvention using spatial diversity, multiple beam receptors are used tocaptures the spatially diverse laser beams.

[0061]FIG. 10 is a block diagram of a RF wireless unit 1000 that can beused as radio frequency (RF) wireless unit 840 (FIG. 8). RF wirelessunit 1000 includes a radio-frequency (RF) wireless transceiver 1040, andan antenna 1050. RF wireless unit 1000 is used for both receiving datain the form of millimeter wave signals, i.e. radio signals, andtransmitting data in the form of millimeter wave signals, i.e. radiosignals. While receiving data, antenna 1040 receives radio signals andprovides the received radio signals to RF wireless transceiver 1040. RFwireless transceiver 1040 converts the radio signals to a QuadratureAmplitude Modulated (QAM) base band electrical signal. Generally, amodulation/demodulation unit (modem) is included in link qualitymanagement unit (see FIG. 13) within media abstraction unit 850 andcoupled to receive the QAM base band electrical signal. The modemdemodulates and decodes the stream of electrical data frames from theQAM base band signal. For embodiments of the present invention usingSONET, SDH, or PDH data format, media abstraction unit 850 implements aPhase Lock Loop (PLL) circuit that recovers a clock signal from theelectrical data stream and generates the SONET/SDH/PDH clock for networksynchronization.

[0062] While transmitting data, the stream of electrical data framesfrom Media abstraction unit 850 is modulated into a QAM base bandelectrical stream, which is then converted to millimeter wave signal byRF wireless transceiver 1040. Antenna 1050 is used to transmit the radiosignal to another network node using RF wireless interfaces.

[0063]FIG. 11(a) is a detailed block diagram of a Packet/TDM crossconnect unit 1100 a, which can be used as Packet/TDM cross connect unit740. Due to the symmetry of receiving and transmitting data withmulti-medium interfaces 410 and 420, Packet/TDM cross connect unit 1100a is often described with reference to a west side and an east sidewhich include the same parts and provide the same functionality.Specifically, Packet/TDM cross connect unit 1100 a includes TDMFramers/Deframers 1110E and 1110W (E refers to East and W refers toWest), dynamic multiplexer/demultiplexers (MUX/DEMUX) 1120E and 1120W,aTDM switch 1130 and a packet switch 1140.

[0064] TDM Framer/Deframer 1110 w is generally coupled to physical layerinterface 810 (FIG. 8) of multi-medium interface 410 (FIG. 7(a)).Incoming TDM frames, such as SONET frames, SDH frames, or PDH frames,are deframed by TDM framer/deframer 1110W. Payload from the TDM frame issent to dynamic multiplexer/demultiplexer 1120W, which demultiplexes thepayload into TDM data and packet data. Dynamic multiplexer/demultiplexer1120W sends TDM payload and packet data to TDM switch 1130 and packetswitch 1140, respectively. TDM switch 1130 determines the destination ofthe various portions of the TDM payload. DROP payload is routed to TDMuser interface 430 (FIG. 7(a)). TDM switch 1130 is configured to receiveADD payload from TDM user interface 430 (FIG. 7(a)) and combines theTHROUGH payload and the ADD payload and sends the resulting TDM payloadto dynamic multiplexer/demultiplexer 1120E.

[0065] Packet switch 1140 determines the destination of each data packetfrom dynamic multiplexer/demultiplexer 1120W. DROP payload data packetsare routed to packet user interface 730 (FIG. 7(a)). Packet switch 1140also receives ADD payload data packets from packet user interface 730(FIG. 7(a)). Packet switch 1140 combines the THROUGH payload and ADDpayload and sends the resulting data packets to dynamicmultiplexer/demultiplexer 1120E. Dynamic multiplexer/demultiplexer 1120Ecombine the packets to form TDM packet columns, i.e. TDM columnscontaining packet data. Then Dynamic multiplexer/demultiplexer 1120Ecombines the TDM payload and the data packets (as described below). Thecombined data is sent to TDM framer/deframer 1110E, which forms a TDMframe, such as a SONET frame, a SDH frame, or a PDH frame, and sends theTDM frame to physical layer interface 810 (FIG. 8) of multi-mediuminterface 420 (FIG. 7(a)). Data received by multi-medium interface 420is processed similarly.

[0066] As mentioned before, the transport payload is packed into thepayload columns of a TDM frame in a column-wise manner. The transportpayload is provisioned in an integral number of columns in the TDMframe. If the TDM frame is not provisioned to full capacity, thenon-provisioned columns are filled with dummy (non-data) characters.Thus, some of the total bandwidth of a TDM network may be unused duringnormal operation. However, with multi-medium network node 700 a or 700 bthe non-provisioned columns can be filled with data packets to fullyutilize the available bandwidth.

[0067]FIG. 11(b) is a block diagram of a Packet/TDM cross connect unit1100 b, which is used in some embodiments of multi-medium network node700 b (FIG. 7(b)). Because Packet/TDM cross connect unit 1100 b issimilar to TDM/cross connect unit 1100 a, the description of unchangedelements is not repeated. However, TDM/cross connect unit 1100 b differsfrom TDM/cross connect unit 1100 a by including multiple TDM/Framer aTDM Framer/Deframer and Dynamic Mux/Demux for each multi-mediuminterfaces of multi-medium network node 700 b. Thus, Packet/TDM crossconnect unit 1100 b includes TDM Framer/Deframers 1110_1W, 1110_2W, . .. 1110_NW, 1110 _1E, 1110_2E, . . . and 1110_ME. Packet/TDM crossconnect unit 1100b also includes dynamic mux/demux 1120_1W, 1120_2W, . .. 1120_NW, 1120_1E, 1120_2E, and 1120_ME.

[0068] As illustrated in FIG. 12, a TDM frame 1200 is divided into threeportions: a header portion 1210, and TDM portion 1220, and a packetportion 1230. TDM frame 1200 can be for example a SONET frame, a SDHframe, or a PDH frame. TDM portion 1220 contains TDM payload and packetportion 1230 contains TDM packet columns holding the data packets. Thenumber of channels having TDM payload determines the sizes of TDMportion 1220 and packet portion 1230. For example, if TDM payload werelarge enough to fill the entire TDM frame, TDM portion 1220 would fillin all columns in the payload columns of TDM frame 1200. Thus, packetportion 1230 would not exist in that particular TDM frame. Conversely,if there is no TDM payload, TDM portion 1220 is not necessary, andpacket portion 1230 can use the entire payload columns of TDM frame1200. In general, TDM portion 1220 has priority over packet portion 1230and packet portion 1230 can be provisioned only in columns that are notprovisioned for the TDM payload.

[0069] Some embodiments of the present invention have different classesof packet data; such has high priority data packets and low prioritydata packets. Generally, high priority packet data has guaranteeddelivery and takes precedence over low priority data packets. Thus, ifthe packet portion 1230 has insufficient capacity to carry both thehigh-priority data packets and the low priority data packets, some ofthe low priority data packets are not sent. The TDM payload commandsprecedence over all types of packet data. Any packet data that is notsent is either dropped or the packet protocols take care ofretransmission at a later time.

[0070] Conventional TDM networks have a pre-defined hierarchy of networkbandwidth and TDM frame size. For example, SONET/SDH/PDH networks onlyallow network bandwidth to be integral multiples of a base bandwidthlike OC-1 and STM-1. The pre-defined hierarchy is suitable for fiberoptic links because fiber optic links have very reliable transmissionquality. However, for wireless links transmission quality can vary dueto a variety of factors such as rain, snow, fog, and electromagneticinterference. Typically, according to the TDM hierarchy, if a givenbandwidth cannot be guaranteed, the connection drops down to the nextpre-defined bandwidth. However, with wireless links, the obtainablebandwidth may be very close to a pre-defined bandwidth. Dropping to thenext highest bandwidth may result in underutilizing the availablebandwidth of the wireless link. For example, multi-medium network nodesconfigured for a SONET/SDH/PDH network using OC-12 speeds (approximately622.08 Mbps) may only be able to support 600 Mbps due to rain. TheSONET/SDH/PDH hierarchy of bandwidths dictates that OC-3 (Approximately155.52 Mbps) speeds be used when OC-12 is not available. By conformingto the SONET/SDH/PDH hierarchy approximately 444.48 Mbps of availablebandwidth is wasted. However, if multi-medium network nodes couldoperate at OC-11.6 the full 600 Mbps bandwidth could be utilized.

[0071] Thus, some embodiments of the present invention are configured tosupport any network bandwidths and are not limited to multiples of abase bandwidth. These embodiments allow a network link to transmit trueTDM frames, such as SONET frames. SDH frames, or PDH frames, atfractional OC-x rates such as in the above example OC-11.6 rate whileconforming to the appropriate TDM requirements such as the GR-253SONET/SDH/PDH/SDH requirements for transport overheads, timing, jitter,alarm conditions etc.

[0072] Media abstraction unit 850 in FIG. 8 on the transmitter sidedetects and determines when a wireless link can be optimized by runningat a fractional OC-x rate. Media abstraction unit 850 packs thetransmission payload into a portion of a standard TDM frame (e.g., aOC-n/STM-n SONET/SDH/PDH/SDH frame), which is just sufficient to allowtransmission at the OC-x rate.

[0073] Specifically, media abstraction unit 850 determines a fractionalpayload size and creates a TDM frame using a transmission payload (TDM,high-priority packets, and low-priority packets) that is less than orequal to the fractional payload size. The shortened payload allows mediaabstraction unit 850 to form a TDM frame, which can be supported by thefractional OC-x rate. For example, the meaningful information is packedinto payload sized up to OC-11.6 rate using TDM frames typically usedfor OC-12 rates. In most embodiments of the present invention, the TDMheader is generated as if the higher data rate is being used. In theseembodiments, the header of the OC-X frame would be identical to theheader of the OC-N frame. Media abstraction unit 850 also chunks thefractional OC-x TDM frame to be transmitted into N M-byte (M being aninteger) radio frames. In one embodiment of the present invention, mediaabstraction unit 850 uses 255-byte radio frames. Generally, the size ofa radio frame is much shorter than that of an STS-n frame becauseshorter frames are less affected by the noise bursts and multi-pathfading occurrences in a dynamic wireless link. Additionally, the errorcorrection efficiency is superior in shorter frames. The radio frames inaddition carry control channel, timing/synchronization, payload(containing fractional OC-x byte stream) and error correction fields.The radio frames are transmitted using a wireless transmit clockgenerator, which is synchronized with the TDM clock. The transmittingsubsystem consists of modem 1030, the RF wireless transceiver 1040 andthe antenna 1050.

[0074] At the receiving end, the incoming stream of radio frames isre-assembled in media abstraction unit 850 to re-create the partiallyfilled OC-x frame. Furthermore, the TDM timing is recovered from theincoming stream to maintain the TDM timing and synchronization. Mediaabstraction unit 850 extends the payload of the OC-X frame to createstandard OC-n/STM-n frame by filling the unfilled portion of the payloadwith stuff bytes. The complete OC-n frames are routed via mediaabstraction unit 850, optical transceivers 820, physical layer interface810 and then multi-medium interface 410 or 420 in FIG. 7.

[0075] As explained above, various conditions can degrade theperformance of wireless links. Therefore, many embodiments of thepresent invention include one or more link quality management unit inmedia abstraction unit 850. The link quality management unit controlsmultiple transmission parameters that adapt the transmission signal of awireless interface to provide more reliable data transmission overchanging link conditions. FIG. 13 is a block diagram of a link qualitymanagement unit 1300. Link quality management unit 1300 controls awireless interface (such as free-space optics unit 830 (FIG. 8) or RFwireless unit 840 (FIG. 8)), which is communicating with a secondwireless interface in another network node. Link quality management unit1300 includes an error correcting code (ECC) unit 1310, a modulationcontrol unit 1320, a transmission power control unit 1340, and a signalquality detector 1350. In general, the transmission signal for thewireless link is received from a Packet/TDM Cross Connect Switch asdescribed above, ECC unit 1310 adds redundancy to the signal in the formof error correction codes. The signal is then modulated in modulationcontrol unit 1320. Transmission power control unit 1340 then determinesthe proper transmission power for the signal, which is sent to thewireless interface as a control signal. The signal then goes to thewireless interface where the transmission power of the signal is set toproper level using the control signal sent by the transmission powercontrol unit before transmission. Received signals are received at thewireless interface. Modulation control unit 1320 demodulates thereceived signal. ECC unit 1310 uses the error correction codes tocorrect errors that may have occurred during transmission and thenprovides the received signal to the Packet/TDM Cross Connect Switch asdescribed above. In some embodiments of the present invention, linkquality management unit 1300 omits modulation control unit 1320. Forexample, if the wireless interface is a free-space optics interface,modulation control unit 1320 is not used.

[0076] On a receiving node, signal quality detector 1350 determines thesignal quality of an incoming signal from a wireless interface of atransmitting node. The signal quality is transmitted back to signalquality detector 1350 of the transmitting node. The signal quality isthen provided to ECC unit 1310, modulation control unit 1320 and/ortransmission power control unit 1340. ECC unit 1310, modulation controlunit 1320, and transmission power control unit 1340 can use the signalquality from signal quality detector 1350 to adapt the transmissionsignal to improve the signal quality. Signal quality detector 1350 canuse different quality measures such as bit error rate, signal to noiseratio, and error vector magnitude.

[0077] Link quality management unit 1300 uses transmission power controlunit 1340 to dynamically adjust the transmission power of the wirelessinterface in a transmitting node, i.e., the node that is transmitting adata stream, to obtain a desired signal to noise ratio (SNR) at thereceiving node to compensate for changing noise conditions on thewireless link. Transmission power control unit 1340 includes a receivedpower level detector 1342 and an accumulator 1344. On a receiving node,i.e. the node that is receiving a data stream, received power leveldetector 1342 of transmission power control unit 1340 measures the powerlevel of the incoming data stream. Received power level detector 1342then compares the measured transmission power level against a thresholdvalue, which may depend on the level of modulation set by modulationcontrol unit 1320, to generate a received power error value. Thereceived power error value is provided to the link quality managementunit on the transmitting node.

[0078] On the transmitting node, accumulator 1344 accumulates thereceived power error level and adjusts the transmission power of thewireless interface on the transmitting node. Specifically, accumulator1344 increments if the transmission power error level is positive anddecrements if the transmission power error level is negative. When thevalue in accumulator 1344 is positive the transmission power level ofthe wireless interface in the transmitting node is increased.Conversely, when the value in accumulator 1344 is negative thetransmission power level of the wireless interface in the transmittingnode is decreased. A problem with increasing transmission power levelsis that interference from the wireless link to other wireless devicesincreases with the transmission power level. Thus, the transmissionpower level must be kept to optimum level enough to avoid interferenceand maintain BER performance.

[0079] Link quality management unit 1300 can also adjust the modulationused in the wireless interface of a transmitting node. Specifically,modulation control unit 1320 adjusts the modulation of the wirelessinterface to maintain a desired signal quality as provided by signalquality detector 1350. For example, in one embodiment of the presentinvention, modulation control unit 1320 selects between quadrature phaseshift keying, and various levels of quadrature amplitude modulation tomaintain a bit error rate of 10-12 or better. When the signal quality isless than the desired signal quality level, modulation control unit 1320decreases the modulation level. Conversely, when the signal quality isgreater than the desired signal quality, modulation control unit 1320increases the modulation level. To prevent constant modulation changes,some embodiments of modulation control unit 1320 are configured toincrease the level of modulation only if the signal quality issignificantly greater than the desired signal quality level. In general,link quality management unit 1300 can adjust the modulation of thewireless interface without causing degradation of the traffic flow onthe wireless link.

[0080] For example, when the bit error rate is greater (i.e. the datastream is of lower quality) than the desired bit error rate, modulationcontrol unit 1320 decreases the modulation level. Conversely, when thebit error rate is less (i.e. the data stream is of higher quality) thanthe desired bit error rate modulation control unit 1320 increases thelevel of modulation. To prevent constant modulation changes, someembodiments of modulation control unit 1320 are configured to increasethe level of modulation only if the bit error rate is significantlylower than the desired bit error rate.

[0081] Link quality management unit 1300 can also improve thereliability of a wireless link by using forward error correctiontechniques. Specifically, in a transmitting node, the outgoing datasignal is encoded using error correction unit 1310, which addsredundancy into the data signal. In the receiving node, the incomingdata signal is decoded using error correction code unit 1310. As thewireless link becomes less reliable, link quality management unit 1300increases the level of redundancy added by error correction code unit1310. Conversely, as the wireless link becomes more reliable, linkquality management unit 1300 decreases the level of redundancy added byerror correction code unit 1310. In general, link quality managementunit 1300 can adapt the level of forward error correction in thewireless interface without causing degradation of the traffic flow onthe wireless link.

[0082] The specific error correction codes used by error correction codeunit 1310 can vary. FIG. 14 shows an embodiment of error correction codeunit 1310 having an error correcting code encoding unit 1430, which usesa dual encoding scheme and thus includes a first ECC encoder 1432 and asecond ECC encoder 1436, as well as a convolution interleaver unit 1434.In a specific embodiment, ECC encoder 1432 first encodes the data streamusing Reed-Soloman codes. Then convolution interleaver unit 1434 is usedto interleave the data at the transmit node so that at the receive nodewhen the data is deinterleaved the errors are spread out and errorbursts are not seen within the data stream. Finally, ECC encoder 1435uses a trellis code to encode the data stream.

[0083] The incoming data stream is decoded by error correction codedecoding unit 1450. Specifically, ECC decoder 1456 decodes the incomingdata stream to correct errors using the redundancy added by ECC encoder1436. Then Convolution deinterleaver unit 1454 counteracts theinterleaving performed by convolution interleaver unit 1434. Finally,ECC decoder 1452 decodes the incoming data stream to correct errorsusing the redundancy added by ECC encoder 1432.

[0084] As the wireless link becomes less reliable, link qualitymanagement unit 1300 uses ECC level control unit 1440 to increase thelevel of redundancy added by error correction code encoding unit 1430.Conversely, as the wireless link becomes more reliable, link qualitymanagement unit 1300 uses ECC level control unit 1440 to decrease thelevel of redundancy added by error correction code encoding unit 1440.Generally, the effectiveness of the error correction is provided to ECClevel control unit by the ECC decoders in error correction code decodingunit 1450. Other embodiments of the present invention may use a singlelevel of error correction code. For example in one embodiment of thepresent invention a single level of REED-SOLOMON error correction codeis used for a free-space optics wireless interface.

[0085] Link quality management unit 1300 can adapt the wirelessinterface using transmission power, modulation level, and forward errorcorrection independently to insure high reliability data transfers overthe wireless link. However, some embodiments of the present inventionuse a more structured approach to selecting the various parameters ofthe wireless interface. For example, in some embodiments of the presentinvention, modulation level is not changed if acceptable performance canbe achieved by modifying transmission power. Similarly, in someembodiments of the present invention, the level of redundancy in theerror correction codes is not modified if acceptable performance can beachieved by modifying modulation level.

[0086] To provide even greater quality of service, some embodiments ofthe present invention integrate link-layer management with network layertraffic management. A variety of techniques are used to provide theintegration of link-layer management with network layer trafficmanagement. For example, as explained above data packets can beprioritized so that during times of limited bandwidth high priority datapackets are sent while low priority data packets are dropped.Specifically, in some embodiment of the present invention, afterinstallation of a multi-medium network node a worse case bandwidth isdetermined for the wireless link. In one embodiment, the worse casebandwidth is the maximum bandwidth that the wireless link can supportduring 99.999% of the operating time of the multi-medium network node.Packet/TDM Cross Connect Switch 740 (FIG. 7(a)) is configured so thatTDM data and high priority packet data is limited to the worse casebandwidth. Because of the integration of the network layer with thephysical layer, low priority packet data can use whatever bandwidth isavailable in each TDM data frame. Specifically, media abstraction unit850 monitors the actual available bandwidth as configured by linkquality management unit 860. The available bandwidth is provided toPacket/TDM Cross Connect Switch 740 which can then form TDM data framesthat can make use of the available bandwidth.

[0087] Furthermore, media abstraction unit 850 can be configured toprovide link quality parameters (e.g. bandwidth, latency) to a trafficmanagement module that can minimize traffic congestion. In a specificembodiment of the present invention, traffic congestion is managed usinga plurality of queues. Specifically, the bandwidth of a link iscalculated based on the link quality of the link. Each level of service(i.e. priority level of data) has a queue with a size that scales withthe available bandwidth.

[0088] In some embodiments of the present invention, media abstractionunit 850 would also inform the network layer traffic manager of linkfailures so that the network layer traffic manager can use the routingprotocols to reroute data around the failed link. Furthermore, in someof these embodiments, the link quality parameters may be used for loadbalancing and other network layer functions.

[0089] Some embodiments of the present invention also includeintelligent network management mechanisms to perform such functions asnew node discovery, network topology determination, linkestablishment/re-establishment, admission controls, network design andplanning, link status monitoring, fault detection, and asynchronouswireless ring protection switching. For example, in one embodiment ofthe present invention, the intelligent network management unit of anetwork node having a wireless interface can automatically discoverother network nodes using wireless interfaces. In addition, insertionand removal of the network nodes with wireless interfaces can beperformed without disrupting other data traffic on the network.Furthermore, the some embodiments of the present invention provideongoing monitoring of wireless links so that smart protection switchingmechanisms can be used in case of link failures. Information for networkmanagement is transmitted using network management control messages,which have the highest priority on the network.

[0090] In some embodiments of the present invention, data packets can betransported using protocols such as Resilient Packet Ring (RPR) toprovide resiliency, efficiency for packet data transport across hybridphysical medium. For example, multiple-medium network node can enableRPR protocols in packet transport. Packets would be encapsulated usingRPR to enable fairness, reliability, efficiency, availability,statistical multiplexing, protection and quality of service (QoS).

[0091] In the various embodiments of this invention, novel structures,systems, and methods have been described to provide a multi-mediumnetwork node configured for use with both TDM data and packet data. Bysupporting multiple medium types such as optical, RF wireless, andfree-space optical wireless, the present invention allows rapiddeployment of the multi-medium network nodes as compared to conventionalnodes require fiber optic links. Furthermore, by combining both TDM dataand packet data into a TDM frame, the present invention provides packetdata service over highly reliable TDM networks and increases thebandwidth utilization of TDM networks. The various embodiments of thestructures and methods of this invention that are described above areillustrative only of the principles of this invention and are notintended to limit the scope of the invention to the particularembodiments described. For example, in view of this disclosure, thoseskilled in the art can define other network nodes, wireless interfaces,wireless links, dynamic multiplexers/demultiplexers, TDMframers/deframers, TDM frames, TDM switches, packet switches, userinterfaces, network topologies, cross connect units, transceivers,physical layer interfaces, media abstraction layers, link qualitymanagement units, error correction code units, error correction codes,signal quality detectors, transmission power control unit, modulationcontrol units, and so forth, and use these alternative features tocreate a method or system according to the principles of this invention.Thus, the invention is limited only by the following claims.

1. A network node for metro area networking comprising: a first wirelessinterface configured for coupling to a second network node; and a linkquality management unit coupled to the first wireless interface andhaving a transmission power control unit; and a first transmissionparameter control unit.
 2. The network node of claim 1, wherein the linkquality management unit is configured to adapt a plurality oftransmission parameters of a transmission signal of the first wirelessinterface to in response to variable link conditions.
 3. The networknode of claim 1, configured to transfer data using time divisionmultiplexing.
 4. The network node of claim 1, further comprising a TDMuser interface configured for data using time-division multiplexing. 5.The network node of claim 1, wherein the transmission power control unitis configured to control a transmission power level of the firstwireless interface.
 6. The network node of claim 5, wherein thetransmission power control unit comprises a received power leveldetector coupled to measure a received power level of an incoming signalreceived by the first wireless interface.
 7. The network node of claim6, wherein the received power level of the incoming signal is comparedto a threshold value to generate a received power error value.
 8. Thenetwork node of claim 7, wherein the received power error value istransmitted to the second network node.
 9. The network node of claim 5,wherein the transmission power control unit comprises an accumulatorcoupled to receive a received power error value from the second networknode.
 10. The network node of claim 9, wherein the transmission powercontrol unit adapts the transmission power of the first wireless nodebased on the received power error value.
 11. The network node of claim1, wherein first transmission parameter control unit is a modulationcontrol unit configured to control the modulation rate of the firstwireless interface.
 12. The network node of claim 11, wherein themodulation control unit comprises a signal quality detector coupled tomeasure a signal quality value of an incoming signal from the secondnetwork node.
 13. The network node of claim 12, wherein the signalquality detector is a bit error detector.
 14. The network node of claim12, wherein the signal quality value is a bit error ratio.
 15. Thenetwork node of claim 12, wherein the signal quality value is a signalto noise ratio.
 16. The network node of claim 12, wherein the signalquality value is an error vector magnitude.
 17. The network node ofclaim 12, wherein the signal quality value is transmitted to the secondnetwork node.
 18. The network node of claim 11, wherein the modulationcontrol unit is coupled to receive a signal quality value from thesecond network node.
 19. The network node of claim 18, wherein themodulation control unit adjusts the modulation of the first wirelessinterface based on the signal quality ratio.
 20. The network node ofclaim 11, wherein the modulation control unit uses quadrature amplitudemodulation.
 21. The network node of claim 20, wherein the modulationcontrol unit uses quadrature phase shift keying.
 22. The network node ofclaim 1, wherein the first transmission parameter control unitcomprises: an error correction unit configured to generate errorcorrection code for the first wireless interface; and an ECC levelcontrol unit coupled to control a level of redundancy in the errorcorrection unit.
 23. The network node of claim 22, wherein the errorcorrect ion unit comprises: a first ECC encoder; and a second ECCencoder coupled to the first ECC encoder.
 24. The network node of claim23, wherein the error correction unit further comprises a convolutioninterleaver unit coupled between the first ECC encoder and the secondECC encoder.
 25. The network node of claim 24, wherein the first ECCencoder is a Reed-Solomon encoder.
 26. The network node of claim 25,wherein the second ECC encoder is a trellis code encoder.
 27. Thenetwork node of claim 1, further comprising a second transmissionparameter control unit.
 28. A network node for metro area networkingusing time division multiplexing, the network node comprising: a firstwireless interface configured for coupling to a second network node; anda link quality management unit coupled to the first wireless interface,wherein the link quality management unit is configured to increase thebandwidth of the first wireless interface when a signal quality value isgreater than a signal quality threshold; and to decrease the bandwidthof the first wireless interface when the signal link quality value isless than the signal quality threshold.
 29. The network node of claim28, wherein the link quality management unit is configured to adapt aplurality of transmission parameters of a transmission signal of thefirst wireless interface to in response to variable link conditions. 30.The network node of claim 28, further comprising a TDM user interfaceconfigured for data using time-division multiplexing.
 31. The networknode of claim 28, wherein the link quality management unit comprises amodulation control unit configured to control the modulation rate of thefirst wireless interface.
 32. The network node of claim 31, wherein themodulation control unit comprises a signal quality detector coupled tomeasure the signal quality value of an incoming signal from the secondnetwork node.
 33. The network node of claim 32, wherein the signalquality detector is a bit error detector.
 34. The network node of claim32, wherein the signal quality value is a bit error ratio.
 35. Thenetwork node of claim 32, wherein the signal quality value is a signalto noise ration.
 36. The network node of claim 32, wherein the signalquality value is an error vector magnitude.
 37. The network node ofclaim 32, wherein the signal quality value is transmitted to the secondnetwork node.
 38. The network node of claim 31, wherein the modulationcontrol unit is coupled to receive the signal quality value from thesecond network node.
 39. The network node of claim 38, wherein themodulation control unit adjusts the modulation of the first wirelessinterface based on the signal quality ratio.
 40. The network node ofclaim 31, wherein the modulation control unit uses quadrature amplitudemodulation.
 41. The network node of claim 40, wherein the modulationcontrol unit uses quadrature phase shift keying.
 42. The network node ofclaim 28, wherein the link quality management unit comprises: an errorcorrection unit configured to generate error correction code for thefirst wireless interface; and an ECC level control unit coupled tocontrol a level of redundancy in the error correction unit.
 43. Thenetwork node of claim 42, wherein the error correction unit comprises: afirst ECC encoder; and a second ECC encoder coupled to the first ECCencoder.
 44. The network node of claim 43, wherein the error correctionunit further comprises a convolution interleaver unit coupled betweenthe first ECC encoder and the second ECC encoder.
 45. The network nodeof claim 44, wherein the first ECC encoder is a Reed-Solomon encoder.46. The network node of claim 45, wherein the second ECC encoder is atrellis code encoder.
 47. A method of controlling a wireless linkbetween a transmitting network node and a receiving network node, themethod comprising: measuring a first signal quality value at thereceiving network node; measuring a second signal quality value at thereceiving network node; providing the first signal quality value and thesecond signal quality value to the transmitting network node adapting afirst transmission parameter to improve the signal quality value; andadapting a transmission power level to improve the second signal qualityvalue.
 48. The method of claim 47, further comprising: measuring a thirdsignal quality value at the receiving network node; and adapting asecond transmission parameter to improve the third signal quality value.49. The method of claim 47, wherein the second signal quality value is areceived power level.
 50. The method of claim 49, wherein the measuringa second signal quality value at the receiving network node, furthercomprises: comparing the received power level with a threshold value;and generating a received power error value as the first signal qualityvalue.
 51. The method of claim 47, wherein the first transmissionparameter is a modulation level.
 52. The method of claim 51, wherein theadapting a first transmission parameter to improve the signal qualityvalue, further comprises decreasing the modulation level when the signalquality value is less than a desired signal quality value.
 53. Themethod of claim 52, wherein the adapting a first transmission parameterto improve the signal quality value, further comprises increasing themodulation level when the signal quality value is greater than a desiredsignal quality value.
 54. The method of claim 47, wherein the firsttransmission parameter is a level of error correction coding.
 55. Themethod of claim 47, wherein the signal quality value is a bit errorratio.
 56. The method of claim 47, wherein the signal quality value is asignal to noise ratio.
 57. The method of claim 47, wherein the signalquality value is an error vector magnitude.
 58. A system for controllinga wireless link between a transmitting network node and a receivingnetwork node, the method comprising: means for measuring a firs t signalquality value at the receiving network node; means for measuring asecond signal quality value at the receiving network node; means forproviding the first signal quality value and the second signal qualityvalue to the transmitting network node means for adapting a firsttransmission parameter to improve the signal quality value; and meansfor adapting a transmission power level to improve the second signalquality value.
 59. The system of claim 58, further comprising: means formeasuring a third signal quality value at the receiving network node;and means for adapting a second transmission parameter to improve thethird signal quality value.
 60. The system of claim 58, wherein thesecond signal quality value is a received power level.
 61. The system ofclaim 60, wherein the means for measuring a second signal quality valueat the receiving network node, further comprises: means for comparingthe received power level with a threshold value; and means forgenerating a received power error value as the first signal qualityvalue.
 62. The system of claim 58, wherein the first transmissionparameter is a modulation level.
 63. The system of claim 62, wherein themeans for adapting a first transmission parameter to improve the signalquality value, further comprises means for decreasing the modulationlevel when the signal quality value is less than a desired signalquality value.
 64. The system of claim 63, wherein the means foradapting a first transmission parameter to improve the signal qualityvalue, further comprises means for increasing the modulation level whenthe signal quality value is greater than a desired signal quality value.65. The system of claim 58, wherein the first transmission parameter isa level of error correction coding.